1. Field of the Invention
This invention relates generally to a two-belt drive system having dual independent damped tensioners with a common pivot, more particularly to a dual tensioner assembly with two torsion springs in a common housing that each bias the position of a pivot-arm to which a belt engaging pulley is rotatably mounted. The tensioner of the invention with its damping mechanism is particularly useful in controlling tension of the multi-V-ribbed belts of a front end accessory drive for automotive or truck engine applications.
2. Description of the Prior Art
Belt tensioners are used to impart a load on a belt. Typically the belt is used in an engine application for driving various accessories associated with the engine. For example, an air conditioning compressor and alternator are two of the accessories that may be driven by a belt drive system. A belt tensioner may include a pulley journaled to an arm which is pivotable on a base. A spring is connected between the arm and a base. The spring may also engage a damping mechanism. The damping mechanism may include frictional surfaces in contact with each other. The damping mechanism damps an oscillatory movement of the arm caused by operation of the belt drive. This in turn enhances a belt life expectancy and the tensioner life expectancy, by minimizing wear on movable components.
Representative of the art is U.S. Pat. No. 6,565,468 to Serkh, U.S. Pat. No. 7,004,863 to Serkh et al., and U.S. Pat. No. 6,582,332 to Serkh, the entire contents of which are all hereby incorporated herein by reference.
Sometimes two belts are used in close proximity on the same engine for example to divide the various accessory loads for improved belt life. In such a case, two tensioners may be used, one for each belt. On the other hand, various tensioner designs have been proposed which simultaneously tension two belts. Representative of the art is U.S. Pat. No. 4,798,564 to Benedict which discloses a single tensioner used to tension a double belt drive, which has a spring-biased primary arm with a secondary arm freely pivoted on the end thereof and having two idler pulleys for simultaneous tensioning of two belts. U.S. Pat. Pub. No. 2003/0159535 A1 to Grover et al. discloses a two belt drive with two identical tensioners stacked one on the other.
Other dual tensioners have been applied to single belt drives which have load reversals, such as starter-generator applications, in order to tensioner either or both of two spans of the same belt. Representative of the art is U.S. Pat. Pub. No. 2002/0039944A1 to Ali, et al. which discloses a tensioner with two mutually biasing tensioner pulleys. Since such tensioners work in concert on a single belt, they have a single torsion spring.